Photographic elements containing synthetic polymeric vehicles

ABSTRACT

NOVEL SYNTHETIC POLYMERS DERIVED FROM POLY(VINYL ALCOHOL) USEFUL AS HARDENABLE GELATIN REPLACEMENTS IN COMPOSITIONS, PHOTOGRAPHIC EMULSIONS AND ELEMENTS, AND A PROCESS FOR PREPARING SAID POLYMERS ARE DISCLOSED.

"United States Patent Office 3,743,627 Patented July 3, 1973 US. Cl.26078.4 D 9 Claims ABSTRACT OF THE DISCLOSURE Novel synthetic polymersderived from poly(vinyl alcohol) useful as hardenable gelatinreplacements in compositions, photographic emulsions and elements, and aprocess for preparing said polymers are disclosed.

This application is a division of our copending application Ser. No.723,279 filed Apr. 22, 1968, now US. Pat. No. 3,637,394.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to new poly(vinyl alcohol) derivatives and a process for theirpreparation. In one aspect, this invention relates to new polymers whichare easily hardened and are compatible with hydrophilic colloids. Inanother aspect, this invention relates to the use of these polymers inphotography and in image-recording elements.

Description of the prior art It is generally known that in thepreparation of imagerecording and light-sensitive elements dispersingagents are needed as vehicles for the light-sensitive materials, forexample, silver halide grains in silver-containing systems. Because ofits good water permeability, thermo reversible gel formation, and otherdesirable properties, gelatin is generally used in whole or in part asvehicles for photographic materials.

Gelatin, however, despite its many good features, has certaindisadvantages. For example, gelatin can be adversely affected by animalor vegetable organisms and environmental changes and in particular,humidity. Further, because gelatin is drived from natural sources, itsquality is variable and its sources of supply are subject to change.Other undesirable features of gelatin include poor dimensional stabilityresulting in the tendency of gelatin films to become brittle uponexposure to air and to shrink causing curling. Gelatin layers cast inemulsion form do not always present a smooth surface due to air bubblesor other foreign matter and, similarly, gelatin layers often appear tobe coated with a haze.

In order to overcome these and other undesirable qualities of gelatin,it is sometimes necessary to include compensatory addenda which, inthemselves, are not always desirable since they can adversely affectsensitimetric quality.

Repeated efforts have been made to replace gelatin with syntheticsubstitutes which do not show these disadvantageous qualities. For manyreasons, no synthetic substance is used more as a gelatin substitutethan poly(vinyl alcohol). The use of poly(vinyl alcohol), however, alsoinvolves certain disadvantages which restrict its application as adispersing agent and binding agent for photographic emulsions.

For example, poly(vinyl alcohol) can be mixed with gelatin only afterprecipitation of silver halide so that in photographic gelatinemulsions, use of poly (vinyl alcohol) as a dispersing agent is somewhatrestricted by the meth- 0d of preparation of the emulsion. In addition,poly(vinyl alcohol) generally is not used as a sole binding agenteffectively.

Previous attempts to prepare hardenable poly(vinyl alcohol) layers frompoly(vinyl alcohol) solution required the addition of products whichwere not satisfactory because they also caused adverse sensitometriceffects and staining.

Other synthetic polymers such as polyacrylamide generally do not impartand exhibit suificient protective or peptizing properties to suspensionprepared therefrom. In addition, the reaction of poly(vinyl alcohol)with various polybasic organic acids or their anhydrides, for example,

aromatic dicarboxylic acids such as phthalic acid and its anhydride isalso known. Unfortunately, however, in employing these acids or theirderivatives, only one of the carboxylic groups enters into the reactionso that the polymers obtained possess the remaining free carboxyl groupand are completely soluble in water as the salts. Since the freecarboxyl group is not a hardening site, these compounds cannotsatisfactorily be used as binding agents or dispersing agents withoutother additives which often adversely affect the sensitometricproperties of the elements.

It has been found to be most desirable to append hardenable sites, suchas primary amino groups, to a poly(vinyl alcohol) moiety forphotographic applications. However, appending such groups has heretoforebeen generally undesirable because of the necessity of employing variousdangerous reagents such as hydrazine in the synthesis with the resultinghazardous working conditions. Furthermore, poor yields, the cumbersomeapparatus required and the undesirable reaction conditions make suchprocedures generally unsuitable, and particularly in the preparation ofvehicles for light-sensitive materials.

It is evident, therefore, that an improved polymer which combines thedesirable characteristics of poly(vinyl alcohol) but which can beconveniently, inexpensively and simply improved by the inclusion ofhardenable sites will greatly enhance the art.

SUMMARY OF THE INVENTION This invention comprises new polymers havingrecurring units which are obtained by partially esterifying poly (vinylalcohol).

One such ester unit derived from the reaction between poly(vinylalcohol) and an aromatic N-carboxy anhydride has a primary amino site.These polymers are compatible with hydrophilic colloids, such asgelatin, are easily hardened and are particularly useful in photography.

One significant feature of this invention is that completely unexpectedresults are obtained using the anhydrides disclosed herein. Normally oneskilled in the art might expect a polymerization reaction involving thesplitting oif of carbon dioxide from the anhydride, resulting in theformation of polyamides. However, enough, this is not found upon thecompletion of our invention, for polyamides are not hardenable underphotographically acceptable conditions and would not give rise tohardenable sites. Instead, upon the addition of a hardener, such asformaldehyde, immediate crosslinking is observed, clearly showing thepresence of hardenable primary amino groups.

Accordingly, it is an object of this invention to provide new polymersof poly(vinyl alcohol) which exhibit desirable combinations of physicalproperties. Another object of this invention is to provide novel andimproved image-recording and light-sensitive compositions. A furtherobject of this invention is to provide novel polymers useful asdispersing agents and which are compatible with hydrophilic colloidsordinarily useful in preparing photosurprisingly I graphic emulsions. Astill further object is to provide layer-forming binding agents forpreparing photographic emulsions.

Other objects of this invention will become apparent from an examinationof the specification and claims that follow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with ourinvention, the above objects are attained with a new poly(vinyl alcohol)polymer comprising recurring units having the formula:

CHz-C H NHR where R is hydrogen or methyl and R is hydrogen, a loweralkyl group desirably containing 1 to 6 carbon atoms, a halogen atomsuch as chlorine, bromine or the like or a nitro group, said recurringunit having a relatively low molecular weight of about 160 to about 240.This recurring unit constitutes from about 1 to about 30 mole percentand preferably about 2 to about 25 mole percent of the polymer.

The novel polymers of this invention are excellent substitutes forhydrophilic colloids and particularly for gelatin in photographicapplications since they exhibit the desirable properties of beingpermeable to processing solutions and are compatible in variouslight-sensitive image recording systems, such as silver halide andnon-silver halide systems. In addition, these polymers exhibitsignificantly less curl than gelatin when formed into layers and placedon various supports. Further, these polymers are easily hardenable withhardeners customarily used to harden hydrophilic colloids. The hardenersinclude, for example, aldehydes, dialdehydes, and the like. These newpolymers can be easily cast into layers forming clear and homogeneousproducts which, unlike gelatin, exhibit no haze or cloudiness. As such,they can be used as a sole binding agent or in combination with othercolloids such as gelatin or even other vinyl polymers.

These novel polymers of our invention can be derived from theesterification reaction between hydroxyl-containing polymers such aspoly(vinyl alcohol) and an aromatic nitrogen-containing carboxyanhydride. Aromatic N-carboxy anhydrides such as isatoic anhydride, alsocalled orthocarboxyphenyl carbamic anhydride, are described in Chemistryof the Amino Acids, John Wiley, vol. 2, pp. 860-862 (1961). In somecases, however, chemical instability of such acids renders theirexistence almost theoretical, whereas their anhydrides, such as isatoicanhydride, are stable and hence available. The nitrogen atom of theisatoic anhydride can be further substituted with a methyl group.Examples of other derivatives of isatoic anhydride useful in preparingthe compounds of the invention include, for example:

4-bromoisatoic anhydride; 6-bromoisatoic anhydride;4-bromo-N-methylisatoic anhydride; 3-chloroisatoic anhydride;5-chloroisatoic anhydride; 5-chloro-N-methylisatoic anhydride;3-nitroisatoic anhydride; 3-nitro-N-methylisatoic anhydride;3-methy1isatoic anhydride; 6-methylisatoic anhydride; 3-propylisatoicanhydride; 3-isopropylisatoic anhydride; and 4-butylisatoic anhydride.

The introduction of the anthraniloyloxy moiety into the side chain ofthe polymer provides an amino group which is an exceptionally goodcrosslinking or hardening site. The hardeners are conveniently thosemost commonly used for hardening other hydrophilic colloids such asgelatin, for example, aldehydes, dialdehydes, dimethylolurea, vinylsulfonyl ethers and other disclosed hereafter. In particular, when thesenovel polymers are included in gelatinemulsion systems, formaldehydeprovides an exceptional hardener for both dispersing agents in a singleaction. By poly(vinyl alcohol), as used in the preparation of thecompounds of this invention, is meant the hydroxyl polymers containing alarge number of recurring intralinear vinyl alcohol UBE-CH L AHJ unitsknown in the art and prepared by polymerizing a vinyl ester, e.g., vinylacetate, vinyl chloroacetate, vinyl propionate, etc., followed bysaponification of the resulting poly(vinyl esters). Other modifyinggroups can be introduced as set forth hereafter.

The poly(vinyl alcohol) starting materials employed in this inventionare generally obtained by hydrolysis of poly(vinyl esters) of loweralkanoic acids such as poly- (vinyl acetate), poly(vinyl propionate) andthe like, although any source of poly (vinyl alcohol) known in the artis acceptable, provided that the material does not contain impuritieswhich cause deleterious photographic effects when employed inphotographic applications.

In practicing this invention, it is convenient to employ compounds ofthe Elvanol poly(vinyl alcohol) series (a trademarked compound of E. I.du Pont de Nemours and Co.). These compounds vary by formula andviscosity, for example, Elvanol 52-22, a medium viscosity, 87-89%hydrolyzed poly(vinyl alcohol), Elvanol 70- 05, a low viscosity,completely hydrolyzed (99l00%) poly(vinyl alcohol), and Elvanol 71-30, amedium viscosity completely hydrolyzed (99-100%) poly(vinyl alcohol).All of these compounds are obtained by the hydrolysis of poly(vinylacetate).

In one embodiment of this invention, we have found that the watersolubility of the poly(vinyl alcohol) polymers such as copoly (vinylalcohol-vinyl anthranilate) can be improved and the chemical behavior ofthe polymer can be rendered amphoteric as shown by examples hereafter.This is accomplished by replacing a minor proportion, that is less than49%, and preferably about from more than 0% to about 15%, of the hydroxygroups with carboxyacyloxy groups. This step involves esterifying saidminor portion of the hydroxy groups, before the reaction between thepolymer and the N-carboxy anhydride, with the following, for example, adicarboxylic acid or the anhydride thereof, such as an aliphaticdicarboxylic acid, e.g., succinic acid, glutaric acid, methylgutaricacid and adipic acid; an unsaturated dicarboxylic acid, e.g., maleicacid, fumaric acid, glutaconic acid, and itaconic acid; an aromaticdicarboxylic acid such as phthalic acid, or a polybasic organic acid.Incorporating such dicarboxylic acids into the polymers of our inventionprovides free carboxylic acid groups which enhance the water solubilityof the polymer and which, in a combination with the amine groups on theanthranilate moiety, renders the polymer amphoteric, i.e., compatible inbasic, as well as acid and neutral media.

In another preferred embodiment of this invention, the above-mentionedpoly(vinyl alcohol) polymer contains recurring units of more than twopolymerizable compounds and preferably three compounds such as aterpolymer comprising poly(vinyl alcohol) and its esters of adicarboxylic acid and N-carboxy anhydride. One such example ispoly(vinyl alcohol-anthranilate-succinate) and still others are setforth hereafter.

The light-sensitive silver halide emulsion of a photographic elementcomprising the polymers of this invention can contain conventionaladdenda such as gelatin plasticizers, coating aids, antifoggants such asthe azaindenes and hardeners such as aldehyde hardeners, e.g.,formaldehyde, mucochloric acid, glutaraldehyde bis(sodium bisulfite),maleic dialdehyde, aziridines, dioxane derivatives andoxypolysaccharides. Sensitizing dyes useful in sensitizing suchemulsions are described, for example, in U.S. Pats. 2,526,632 of Brookerand White issued Oct. 24, 1950, and 2,503,776 of Sprague issued Apr. 11,1950. Spectral sensitizers which can be used are the cyanines,merocyanines, complex (trinuclear) cyanines, complex (trinuclear)merocyanines, styryls, and hemicyanines. Developing agents can also beincorporated into the emulsion if desired or can be contained in aseparate underlayer. Various silver salts can be used as the sensitivesalt such as silver bromide, silver iodide, silver chloride, or mixedsilver halides such as silver chlorobromide or silver bromoiodide. Thesilver halides used can be those which form latent images predominantlyon the surface of the silver halide grains or those which form latentimages inside the silver halide crystals such as described in U.S. Pat.2,592,250 of Davey and Knott issued Apr. 8, 1952.

The silver halide emulsion layer of a photographic element comprisingour novel polymers can contain any other of the hydrophilic,water-permeable binding materials suitable for this purpose. Suitablematerials include gelatin, colloidal albumin, polyvinyl compounds,celluose derivatives, acrylamide polymers, etc. Mixtures of thesebinding agents can also be used. The binding agents for the emulsionlayer of the photographic element can also contain other dispersedpolymerized vinyl compounds. Such compounds are disclosed, for example,in U.S. Pats. 3,142,568 of Nottorf issued July 28, 1964; 3,193,386 ofWhite issued July 6, 1965; 3,062,674 of Houck, Smith and Yudelson issuedNov. 6, 1962; and 3,220,844 of Houck, Smith and Yudelson issued Nov. 30,1965; and include the waterinsoluble polymers of alkyl acrylates andmethacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates andthe like.

The silver halide emulsion comprising our novel polymers can be coatedon a wide variety of supports. Typical supports are cellulose nitratefilm, cellulose ester film, poly(vinyl acetal) film, polystyrene film,poly(ethylene terephthalate) film and related films or resinousmaterials as well as glass, paper, metal and the like. Supports such aspaper which are coated with alpha-olefin polymers, particularly polymersof alpha-olefins containing two or more carbon atoms, as exemplified bypolyethylene, polypropylene, ethylene-butene copolymers and the like canalso be employed.

Photographic emulsions comprising our polymers can also containspeed-increasing compounds such as quaternary ammonium compounds,polyethylene glycols or thioethers. Frequently, useful effects can beobtained by adding the aforementioned speed-increasing compounds to thephotographic developer solutions instead of, or in addition to, thephotographic emulsions.

The novel polymers of our invention can be used in photographic elementsand in various kinds of photographic systems. In addition to beinguseful in X-ray and other nonoptically sensitized systems, they can alsobe used in orthochromatic, panchromatic and infrared sensitive systems.The sensitizing addenda can be added to photographic systems before orafter any sensitizing dyes which are used.

The polymers of the invention can be used in emulsions intended forcolor photography, for example, emulsions containing color-formingcouplers or emulsions to be develped by solutions containing couplers orother color-generating materials, emulsions of the mixed-packet typesuch as described in U.S. Pat. 2,698,794 of Godowsky issued Jan. 4,1955; in silver dye-bleach systems; and emulsions 6 of the mixed-graintype such as described in U.S. Pat. 2,592,243 of Carroll and Hansonissued Apr. 8, 1952.

Silver halide emulsions containing the novel polymers of the instantinvention can be sensitized using any of the well-known techiques inemulsion making, for example, by digesting with naturally active gelatinor various sulfur, selenium, tellurium compounds and/or gold compounds.The emulsions can also be sensitized with salts of noble metals of GroupVIII of the Periodic Table which have an atomic weight greater than 100.

The gelatin substitutes described herein can be employed as the bindingagent in one or more layers of a photographic silver halide element.However, photographic silver halides are generally precipitated in thepresence of binding agents such as gelatin or other colloids whichexhibit very good peptizing action. Therefore, the photographic silverhalide emulsions or layers of this invention will generally contain somebinding agent such as gelatin which exhibits this very good peptizingaction. Generally, the concentration of the polymers described herein asgelatin substitutes will be in the range of more than 0% and from about10 to about 95%, often in the range of about 50 to about 95 by weight,based on total binding agent (dry weight), employed in photographicemulsions, photographic emulsion layers or other layers of aphotographic element. In the preferred case, the remainder of thebinding agent is gelatin, although other colloids also give goodresults. Where the polymers are used in photographic elements in layersother than the emulsion layers, for example, in filter layers,antihalation layers, antiabrasion layers, antistatic layers, barrierlayers, receiving layers for diffusion transfer processes and the like,they can be used as the sole vehicle or in admixture with natural orsynthetic colloids such as are mentioned hereinbefore. The silver halideemployed in the preparation of light-sensitive coatings described hereinincludes any of the photographic silver halides as exemplified by silverbromide, silver chloride and silver iodide, silver chlorobromide, silverbromoiodide and the like. Very good results are obtained with highcontrast silver halide emulsions in which the halide comprises at least50 moles percent chloride. Preferred emulsions of this type contain atleast 60 mole percent chloride, less than 40 mole percent bromide andless than 5 mole percent iodide.

Silver halide emulsions containing the polymers of the invention can beused in difiusion transfer processes which utilize the undevelopedsilver halide in non-image areas of the negative to form a positive bydissolving the undeveloped silver halide and precipitating it on areceiving layer in close proximity to the original silver halideemulsion layer. Such processes are described in U.S. Pats. 2,352,014 ofRott issued June 20, 1944; 2,543,181 of Land issued Feb. 27, 1951; and3,020,155 of Yackel, Yutzy,

- Foster and Rasch issued Feb. 6, 1962. The emulsions can also be usedin diffusion transfer color processes which utilize a diffusion transferof an imagewise distribution of developer, coupler or dye, from alight-sensitive layer to a second layer, while the two layers are inclose proximity to one another.

The following examples are included for a further understanding of theinvention.

EXAMPLE 1 Preparation of copoly(vinyl alcohol-vinyl anthranilate) 7EXAMPLE 2 Preparation of poly(vinyl alcohol-vinyl anthranilatemonovinylsuccinate) A solution of 132 g. of poly(vinyl alcohol) (Elvanol 52- 22)in 1300 ml. of dimethyl sulfoxide is prepared at 98 C., then cooled toroom temperature. A solution of 30 g. of succinic anhydride in 100 ml.of dimethyl sulfoxide is added dropwise and the reaction mixture stirredon the steam bath for about two hours. The solution is again cooled toroom temperature, then treated with 2 ml. of triethylamine followed by49 g. of isatoic anhydride in 300 ml. of dimethyl sulfoxide. The mixtureis again heated on the steam bath to complete the reaction. Theresulting polymer is isolated by precipitation, washed in acetone andthen dissolved in water containing a few milliliters of 10% sodiumhydroxide. This polymer shows desirable solubility on both sides of anisoelectric region near a pH of 5.25 indicating the presence of bothprimary amino groups and free carboxylic groups. The rapid gelation ofthis polymer with formaldehyde confirms the presence of the primaryamino group.

EXAMPLE 3 In order to determine the effectiveness of the polymerpoly(vinyl alcohol-vinyl anthranilate-monovinyl succinate) as adispersing medium in a light-sensitive element, a sample of said polymeris incorporated into a photographic coating as described hereafter.

A portion of a sulfur and gold sensitized silver bromoiodide gelatinemulsion containing 11 g. of gelatin/Ag mole and weighing 1500 g./Agmole is melted and held for 0, 15 and 30 minutes respectively at atemperature of 65 C. The portion of the above emulsion which is not heldat 65 C. is divided into four parts. To each of two parts is added 219g. of gelatin, resulting in a total of 230 g. of gelatin per mole Ag foreach part. To the two remaining parts is added 219 g. ofpoly(vinylaloohol-vinyl anthranilate-monovinyl succinate), as preparedin Example 2, each part now having a total of 230 g. of gelatin andpolymer per mole Ag. To one of the gelatin and polymer parts and to oneof the all gelatin parts is added 6.0 ml. of a 10% formaldehyde solutionper mole Ag. No hardener is added to the other parts.

Those portions of the original emulsion which are held at 65 C. for 15and 30 minutes respectively are divided and treated according to theprocedure described above.

The gelatin and poly(vinyl alcohol-vinyl anthranilatemonovinylsuccinate) used herein are added as 10% and 8.75% aqueous solutionsrespectively.

These melts are coated on a poly(ethylene terephthalate) film support at381 mg. Ag./ft. and 811 mg. vehicle/ ftfl.

The coating variations are tabulated as follows:

Do. Formaldehyde.

These coatings are now exposed imagewise and developed for about 5minutes in Kodak DK-SO developer,

fixed, washed and dried. The coating containing a major proportion ofpolymer and a minor proportion of gelatin which is not treated withformaldehyde is washed off during processing due to its inability towithstand the alkaline environment and increased temperature of theprocessing solutions. However, similar coatings to which formaldehydehas been added do not wash off. The results show that the polymers ofthe invention contain active hardening sites capable of reacting with aconventional hardening agent such as formaldehyde. The hardened samplescontaining polymers of the invention exhibit far less curl than thosecontaining only gelatin. In addition, they are clear and without haze,are permeable to processing solutions, exhibit good sensitornetricqualities such as the absence of fog, loss of speed and density, andhave a very smooth surface.

EXAMPLE 4 Copoly(vinyl alcohol-vinyl N-methylanthranilate) A solution of22.1 g. of polyvinyl alcohol (Elvanol 7005) in 225 ml, of dry, distilleddimethyl sulfoxide is prepared at C. A solution of 0.2 g. of sodiumhydroxide dispersion (50% in a mineral oil) in 25 ml. of dry dimethylsulfoxide is added with stirring. A solution of 8.9 g. (0.05 mole) ofN-methylisatoic anhydride in 25 ml. of dry dimethyl sulfoxide is addedcausing a vigorous expulsion of carbon dioxide. Stirring at 95 C. iscontinued for about three hours and the resulting polymer isprecipitated and washed thoroughly in isopropyl alcohol. Dried in vacuoat 50 C., the yield is 27.8 g. (97% of theoretical).

.EXAMPLE 5 The above Example (4) is repeated using 0.3 ml. oftriethylamine as a catalyst and although the reaction is less vigorousand more controllable, the product yield equals the theoretical amount.

EXAMPLE 6 Poly(vinyl alcohol-vinyl-N-methylanthranilatemonovinylsuccinate) To a solution of 246 g. of poly(vinyl alcohol) (Elvanol71-30) in 7600 ml. of distilled dimethyl sulfoxide at 98 C., 60 g. (0.6mole) of succinic anhydride in 200 ml. of dimethyl sulfoxide is addedwith stirring. This solution is stirred at 95 C. for about two hours.The 4 ml. of triethylamine and 106.2 g. (0.6 mole) of N-methylisatoicanhydride in 600 ml. of dimethyl sulfoxide are added and stirring iscontinued for about three hours more. The polymer is precipitated andwashed thoroughly in isopropyl alcohol and stored damp.

EXAMPLE 7 In an example similar to that described more fully in Example3, the effectiveness of the alkyl substituted anthranilate polymer in alight-sensitive element is determined. These results clearly show thatsaid polymers harden, and resist abrasion and Washing-0E duringprocessing which evidence is indicative of the presence of hardenablesites which are easily crosslinked with a hardener (formaldehyde).

These examples show that the polymers of the invention are supreior togelatin in flexibility, abrasion resistance, and in dimensionalstability. Further, these polymers are compatible with gelatin inphotographic emulsion layers and they can be hardened with the samehardening agents as gelatin under the mild conditions required in aconventional photographic emulsion layer.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected withoutdeparting from the spirit and scope of the invention as describedhereinbefore and in the appended claims.

9 10 We claim: acting the resulting reaction product with an aromaticN- 1. A hardenable poly(vinyl alcohol) copolymer concarboxyanhydride soas to yield a terpolymer comprising sisting essentially of recurringunits of vinyl alcohol and from about 1 to about 30 mole percentrecurring units from about 30 mole percent to about 1 mole percentrehaving the formula curring units having the formula 5 --CH CH- CHg-C L6 L I .J

=0 l 10 NHR NHR 15 where R is hydrogen or methyl and R is hydrogen, aWhere R 15 hydrogen thyl and R 1s hydrogen, a lower alkyl group, ahalogen atom or a nitro group. lower alkyl group a halPgen atom 9 agrouP- 2. A hardenable poly(vinyl alcohol) copolymer as set F F P clamWherem 531d Polycarboxyhc forth in claim 1 wherein said copolymercomprises coacld 1s succlmc acld' Po1y(viny1 alcoholwinyl anthranilate)2 8. The process of claim 6, wherein said N-carboxyan- 3. A hardenablepoly(vinyl alcohol) copolymer conhydndc IS an N-methyllsafiowanhydmlesisting essentially of recurring units of vinyl alcohol, from PP q of clam} Wherem 531d about 0 mole percent to about 15 'mole percentrecurring anhydnde 1S lsatolc anhydndeunits of vinyl alcohol esterifiedwith an organic polycarboxylic acid, and from about 30 mole percent toabout 1 5 References Cited mole percent of recurring units of vinylalcohol esterified UNITED STATES PATENTS With an aromaticN-carboxyanhydride. 2 94 10 8 19 0 Merrill et 1 96 33 4. A polymer asset forth in claim 3, wherein said aro- 3,000,741 9/1961 De Pauw et aLmatic N-carboxyanhydride is isatoic anhydride.

5. A polymer as set forth in claim 4, wherein said poly- 30 JOSEPH LSCHOFER, P i E i carboxylic acid is succinic acid.

6. A process for preparing a hardenable terpolymer KIGHT AsslstantExammer U.S. C1. X.R.

of poly(vinyl alcohol), said process comprising first esterifying lessthan 49 mole percent of the alcohol with a polycarboxylic acid oranhydride, and subsequently re- 96-88; 260-785 T, 91.3 VA

